1. Field of the Invention
This invention relates to anaerobic sludge digesters and more particularly to a sludge digester having network means submerged therein for positively displacing sludge containing active bacteria to quiescent zones of the digester so as to insure active digestion of the entire digester contents.
2. Prior Art
In the bacteriological digestion of sludge, it has long been known that some mixing or agitation of the digester contents during the digestion process serves to distribute the raw sludge among the bacteria, to minimize settling of mineral solids or grit and to maintain uniform chemical and thermal conditions, thus to extend the area of active bacterial action throughout the available volume in the tank. Originally it was felt that the mixing caused by natural gasification and its resulting uplift was sufficient. More recently supplementary mechanical mixing has been used to enhance the benefits derivable from a good distribution of the raw sludge among the bacteria. Existing mixing and agitation systems can be divided into three basic types: mechanical stirrers, external impellers and gas uplifters. The mechanical stirrers have problems resulting from hair and other stringy solids tending to foul the moving parts in the tank. External impellers have a drawback in that they draw from or pump to only a few points in the digester, thus allowing short-circuiting to occur between inlet and outlet points of the digester and leaving large areas of unmoved sludge. Gas mixing systems have a similar drawback in that they tend to short-circuit and produce the desired mixing in only limited areas of the digester tank.